An acoustic transducer or speaker such as an ultrasonic emitter can be used to determine the location of items that contain acoustic microphones such as an ultrasonic receiver. For example, existing devices such as smartphones are capable of receiving ultrasonic signals in order to establish their presence or location within a retail, factory, or warehouse environment. The ultrasonic emitter can transmit ultrasonic energy in a short burst which can be received by an ultrasonic transducer (microphone) in the ultrasonic receiver (e.g. smartphone), thereby establishing the presence of the device within the environment.
Further, the use of several ultrasonic emitters distributed within the environment can also be used to provide a specific location of a particular device using techniques known in the art such as triangulation, trilateration, and the like. However, unlike radio frequency locationing systems, ultrasonic locationing systems suffer from particular problems related to the characteristics of ultrasonic sound waves and their environment of use. For example, ultrasonic signals are easily subject to noise. In particular, broadband noise events (which are typical of impact noise) can fall within the frequency band of interest, and cannot be filtered out without also filtering the desired signal. As a result, accurately triggering a location measurement using an incoming pulse in a flight time based locationing system can be difficult for amplitude based detectors if there are a lot of in-band noise events that could result in false triggers. Detectors of single pulses are very susceptible to impact noise or noise tones greater in length than the pulse period. Moreover, the selectivity of a very short Fast Fourier Transform (FFT) or a Goertzel algorithm run on a single pulse can be poor, i.e. the system is susceptible to tones at nearby frequencies.
Therefore, ultrasonic locationing systems rely on high sound pressure level (SPL) pulses being sent from acoustic transducers in order to overcome the above issues. Using high SPL requires high electrical powers to drive the acoustic transducers to the necessary levels. However, this high intensity burst has been shown to change the characteristics of the transducer during its initial burn-in time in the early stages of its life until it settles into its normal performance. In addition, after its settling time, it has been shown that the transducer's response will continue to decline over time (change its sensitivity, impedance, etc).
Accordingly, there is a need for an improved technique to resolve the above issues with acoustic transducer aging. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing background.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.
The apparatus and method components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.